trunk only: preserving context (src files)

Pat Rankin wrote:
> collect them all into some new struct and
> save that separately rather than jamming more non-option stuff
> into struct flags.

This patch:
- collects all context/tracking related fields from flags
  into a new structure called "context."
It also adds the following to the new structure:
- stethoscope turn support
- victual support
- tin support

src/exper.c

@@ -105,7 +105,7 @@ more_experienced(exp, rexp)
 #ifdef SCORE_ON_BOTL
 	   || flags.showscore
 #endif
-	   ) flags.botl = 1;
+	   ) context.botl = 1;
 	if (u.urexp >= (Role_if(PM_WIZARD) ? 1000 : 2000))
 		flags.beginner = 0;
 }
@@ -161,7 +161,7 @@ const char *drainer;	/* cause of death, if drain should be fatal */
 
 	if (u.uexp > 0)
 		u.uexp = newuexp(u.ulevel) - 1;
-	flags.botl = 1;
+	context.botl = 1;
 }
 
 /*
@@ -214,7 +214,7 @@ boolean incr;	/* true iff via incremental experience growth */
 	    adjabil(u.ulevel - 1, u.ulevel);	/* give new intrinsics */
 	    reset_rndmonst(NON_PM);		/* new monster selection */
 	}
-	flags.botl = 1;
+	context.botl = 1;
 }
 
 /* compute a random amount of experience points suitable for the hero's